The instant invention relates to circular warp-knit composite fabrics and cords, and more particularly to a shaped (multi-sided) warp-knit cord having selected types of yarn localized on selected side surfaces of the shaped cord to provide the selected side surfaces of the cord with particular surface characteristics attendant to the localized yarn materials.
Shaped cords, such as used for packing materials, have heretofore been known in the art. The term "shaped" as used within this specification is intended to encompass all types of cords, packings, etc. having a non-circular cross-section, and/or having at least one flat surface, such as in a square or triangular cross-section. With regard to known prior art, the U.S. Pat. No. 239,287to Winans ; Blaisdell U.S. Pat. No. 1,771,912; and Webster et al U.S. Pat. No. 3,124,032 represent different types of shaped packing materials. In the context of the invention, it is worthwhile to note that each of the packing materials described in these patents is formed by a braiding method and has uniform exterior surface properties on all sides. While these types of braid configurations are adequate for the intended purpose, it has been found that there is a need for a shaped, or multi-sided cord or packing material, wherein a single type of yarn material can be localized on a given side of the cord, while other yarn materials are localized on the other sides. For example in a packing cord, it would be advantageous to be able to provide a specialized Teflon yarn material on the inner side of the packing which engages the rotating shaft, and to utilize other less expensive materials on the other sides of the packing which do not contact the shaft. Such a configuration would utilize less of the more expensive Teflon materials and reduce the overall cost of such products. In general, braiding procedures utilize a single type of yarn wherein during braiding the yarns migrate around the periphery of the braid to provide a uniform distribution of yarns throughout the braid. Different types of yarns can be utilized in the braid. However, since the yarns are uniformly distributed during braiding, the exterior surface properties are uniform across all sides of the braid configuration. Because of the uniform yarn distribution in a braided material, the desired localized material configurations are impossible to achieve in a braiding method.
The instant invention provides the desired shaped cord construction having localized distributions of yarns on selected sides of the cord. The shaped cord of the present invention is formed using a circular warp-knitting method wherein selected types of yarns are grouped together and rotated in such a manner that yarns of the same type of material are repeatedly located in the same knitting position for each knitted course. Shaping of the cord is accomplished by selectively locating interlace yarns around the circumference of the cord construction. For example, four equally circumferentially spaced interlace yarns will form a square knit configuration having four distinct sides when viewed in cross-section.
Accordingly, among the objects of the instant invention are: the provision of a multi-sided (shaped) warp-knit cord wherein selected types of yarns are localized on selected sides of the shaped cord to provide one exterior surface of the cord with a particular type of yarn material and other exterior surfaces with another type of material; the provision of a square-shaped cord having a selected yarn type localized on one of the four sides of the cord; and the provision of a square-shaped cord having a selected yarn type localized on two opposing sides of the cord.